Satellite very small aperture terminals (VSATs) transmit packet data in a time division multiple access (TDMA) type. The satellite VSATs control a signal level at the time of transmitting the packet data. In spite of minute control, the signal level control has a direct influence on baseband performance, that is, transmission performance.
Meanwhile, when the satellite VSATs receive continuous stream data such as satellite broadcasts, they can easily control the signal level. However, when the satellite VSATs receive burst data, the satellite VSATs detect power through automatic level control (ALC) to control the signal level. In this case, inaccuracy in power detection and power loss by a cable and the like also influence the transmission performance of the satellite VSAT.
As such, when the power level is not accurately controlled, the satellite VSATs should consider adjacent channel interference, a problem in that a solid state power amplifier (SSPA) operates in a non-linear section, and the like. Therefore, the satellite VSATs require a lot of back off at the time of transmitting the packet data. If the back off of the transmission power is not a lot, it influences the interference of the adjacent channel Moreover, when the same/adjacent channel interference occurs even in a multi-beam satellite repeater, polarization reuse, and the like in addition to a single-beam satellite repeater, power is not balanced, thus causing interference.
In particular, when the satellite VSATs operate in a linear modulation type, the above-mentioned influence is exerted to the transmission performance. Contrary to this, techniques such as frequency shift keying (FSK), minimum shift keying (MSK), and continuous phase modulation (CPM) as the non-linear modulation type are not better than the linear modulation type in transmission efficiency per bandwidth, but less influence the adjacent channel interference. That is, although imbalance in power with the adjacent channel occurs, the interference influence decreases.
Meanwhile, the transmission performance and price of the satellite VSATs are influenced depending on an outdoor unit (ODU). Further, the outdoor unit (ODU) is significantly influenced by temperature, surrounding conditions, part price, an antenna installation location, and the like.
Therefore, it is difficult for a private person to purchase and install the satellite VSAT in person and is problematic in that maintenance for the satellite VSAT should be performed at the time of changing his/her residence. Further, when maintenance is not performed, a subscriber is in an outage state in terms of a network.